Waste treatment of fluoroborate solutions

ABSTRACT

A two-step process for the waste treatment of fluoroborate solutions which involves hydrolysis at an acidic pH in the presence of calcium ions toliberate fluoride and subsequent removal of fluoride values, e.g. by precipitation as calcium fluoride under alkaline conditions.

This is a division of application Ser. No. 602,180, filed Aug. 5, 1975,now U.S. Pat. No. 4,008,162.

BACKGROUND OF THE INVENTION

Plating solutions, and the like, containing metal fluoroborates andfluoroboric acid now enjoy a great deal of popularity in the metalfinishing industry. Indeed, in some areas, such as printed circuitmanufacture, no viable substitutes for the fluoroborate plating bathsare currently available. However, at this time, no effective system isknown for waste treatment of spent baths and rinse waters containingfluoroborate. Most current treatment systems for this species functionon a simple neutralization followed by discharge. This type of treatmentseldom, if ever, accomplishes more than a conversion of the fluoroborateion to a hydrated boron trifluoride or hydroxyfluoroborate anions. Thesespecies when discharged are then free to slowly hydrolyze and releasetoxic fluoride ion into the environment as hydrofluoric acid.

Indeed, previous work (Tomio Onishi, Bulletin of the Chemical Society ofJapan, Vol. 42, No. 1, pp. 127-131, 1969) indicates that fluoroboratedischarged into streams, rivers, and ocean waters may require more thana year to undergo complete hydrolysis. Additionally, it is reported inthe same study, that conditions of elevated pH and temperature canreduce the time required for complete decomposition of the fluoroboratespecies to a period of 20 to 30 hours. However, a treatment retentiontime of this magnitude for fluoroborate hydrolysis is extremelyimpractical for most operations.

It is therefore an object of the present invention to provide a new andimproved process for the hydrolysis of fluoroborate ions.

It is another object of the present invention to provide a process foreffectively removing fluoride values from solutions containingfluoroborate compounds.

It is still another object of the invention to provide a process fortreatment of spent fluoroborate processing solutions from a metalfinishing operation.

A further object is to provide a process for the pollution free disposalof effluents from a metal finishing operation employing fluoroboratesolutions.

These and other objects of the present invention will become apparent tothose skilled in the art from the detailed description and illustratedembodiments thereof.

In the drawings:

FIGS. 1-3 are schematic flow diagrams depicting respectively batch,flow-through and integrated treatments of waste solutions containingfluoroborate compounds.

FIGS. 4-7 are graphical representations showing the effects of operatingvariables on the fluoroborate ion hydrolysis rate.

THE INVENTION

The present invention relates to a novel process which greatly reducesthe time required for hydrolysis of the fluoroborate ion and otherspecies intermediate in total hydrolysis of fluoroborate compounds likehydrated boron trifluoride and hydroxy fluoroborate anions. For thepurpose of this application the term "fluoroborate" is meant also toinclude any such intermediary compounds and anions. It has beendiscovered that if solutions containing fluoroborate are heated at anacid pH in the presence of calcium ions, then a more rapid hydrolysis ofthe fluoroborate is achieved than with any other prior art method. Infact, it is possible to substantially completely hydrolyze thefluoroborate in 1 hour or less.

The liberated fluoride, hydrofluoric acid and calcium fluoride formed inthis reaction can then be treated by any number of techniques known inthe art for removal of fluoride values from solution. For the purpose ofthis application the term "fluoride values" is intended to include theaforementioned liberated fluoride, hydrofluoric acid and calciumfluoride. One such applicable method involves neutralization of thesolution with an alkaline compound and precipitation of fluoride ascalcium fluoride under alkaline conditions. Although hereinafter onlythis approach of removing fluoride values from solution will bediscussed it should not be construed as a restriction of the scope ofthe invention. Thus, a treatment system for hydrolysis of fluoroborate,with subsequent neutralization and fluoride removal, can be described bythe following two equations: ##EQU1##

There are three main variables affecting the fluoroborate hydrolysisreaction rate (1): namely calcium ion concentration, temperature and pH.

The calcium ion concentration is expressed hereinafter in terms of amultiple of the potential molar fluoride values (PMFV) of the solutionsassuming complete hydrolysis. Referring to equations (1) and (2) it isseen that a stoichiometric amount of calcium ions is 0.5 times thepotential molar fluoride value depicted in reaction (1) as HF. It shouldbe understood that in case the fluoroborate solution to be treated alsocontains "free" fluorides, such as hydrofluoric acid or fluoride ions,determination of PMFV would also take into account the concentration ofsuch fluorides. It was found that performing the hydrolysis reaction inthe presence of calcium ions, even in very small concentrations, greatlyenhances the hydrolysis rate, for instance provisions of calcium ions ata concentration of only 0.25 PMFV causes an increase in the hydrolysisrate of about 55 percent as compared to a reaction carried out underidentical conditions but in the absence of calcium ions. It is thereforebelieved that provisions of calcium ion in any concentration is helpfulin accelerating the hydrolysis reaction. For optimum enhancement, i.e.to achieve substantially complete hydrolysis in very short times, it ispreferred that the amount of calcium ion concentration provided be atleast about 0.5 PMFV or higher. There is no critical upper limit for thecalcium ion concentration, however for practical purposes theconcentration usually need not exceed a value of about 1.5 PMFV. Avariety of calcium compounds may be used as the source of the calciumions, such as calcium hydroxide, calcium oxide, calcium chloride and thelike. The only limitation as to the nature of the calcium compound isthat it should display sufficient solubility under acid conditions so asto provide "free" calcium ions to aid in the breakdown of thefluoroborate.

The hydrolysis reaction may also be operated in such a fashion that apredetermined "excess" of calcium ions is maintained in solution bymanual or automated monitoring and addition means. In practice, thiswould reduce to maintenance of a calcium ion concentration above thataccounted for by the solubility of calcium fluoride under the hydrolysisconditions prevailing in the system. In this manner it is assured thatat least the stoichiometric amount of calcium ions is provided, which isnecessary for the complete potential precipitation of the fluoroborateloading. As an example, in a system where conditions affecting calciumfluoride solubility as well as fluoroborate loading are relativelyconstant, an excess of a few milligrams of calcium ions per liter ofsolution would be sufficient. In other circumstances, where conditionsaffecting the solubility of calcium fluoride are subject to fluctuationsand/or where shock loading may occur, it is preferred to maintain a muchlarger excess of calcium ions.

The hydrolysis reaction should be carried out under acid conditions. Itwas found that even at very slightly acidic conditions, e.g. at a pH of6.2, the hydrolysis rate was significantly improved as compared to therates obtained at slightly alkaline conditions. The preferred conditionsfor the hydrolysis reaction is at a pH of about 4.0 or less and mostpreferably in the pH range from about 1.0 to about 3.0. Operation inthis latter range will result in substantially complete hydrolysiswithin a very short time such as 1 hour or less. If needed, the pH isadjusted during the reaction by addition of a suitable metal hydroxide,oxide or carbonate, e.g. calcium hydroxide, to raise the pH, or by theaddition of an appropriate mineral acid, such as hydrochloric, nitric,sulfuric acid and the like to lower the pH. A preferred treatmenttechnique would be to add sufficient quantities of hydrochloric acid andcalcium hydroxide to maintain the desired pH and to provide the calciumions necessary to promote the hydrolysis of the fluoroborate species. Asthe calcium ion combines with the hydrofluoric acid released fromfluoroborate, new calcium ion provided as calcium chloride according toreaction (3):

    HF + HCl + Ca(OH).sub.2 →1/2CaCl.sub.2 + 1/2CaF.sub.2 + 2H.sub.2 O (3)

for any particular system, the required amounts of hydrochloric acid andcalcium hydroxide can easily be determined by a person with ordinaryskills in the art.

The reaction should be carried out at elevated temperatures. It wasfound that at temperatures above room temperature the hydrolysis ratewas significantly improved, for instance the percent hydrolysis after 4hours was about doubled at 130° F. and tripled at 160° F. The preferredtemperature range is from about 160° F. to about the boiling point ofthe reaction mixture, with the range of from about 180° F. to about 200°F. being the most preferred since substantially complete hydrolysis canbe achieved in this temperature range in less than 1 hour's time.

Experimental results have shown that a substantially completefluoroborate hydrolysis is accomplished in 1 hour or less when theaforementioned preferred operating conditions are maintained. However,it is anticipated that some redundancy would be provided in a commercialsystem; therefore, a retention time in the range of about 1 to 2 hoursor even higher would be employed in such a system.

Regardless of what system is used, the treatment solution should beproperly agitated to insure intimate contact of participant reactants inthe hydrolysis reaction. Also, since some amount of liberatedhydrofluoric acid can be volatilized at the elevated temperature, thereaction should be carried out in a closed vessel, which is suitablyvented to a fume scrubbing device or to the vessel, in which reaction(2) is being conducted.

After hydrolysis, the removal of the fluoride values from the reactionsolution in accordance with reaction (2) involves neutralization offreed acid and precipitation of fluoride at alkaline conditions. Thiscan be accomplished by timely addition of a metal hydroxide, oxide orcarbonate. Suitable metal hydroxides, oxides or carbonates include thoseselected from alkali or alkaline earth metal hydroxides, oxides orcarbonates. Of the latter, calcium hydroxide or oxide is the mostpreferred. In case the hydrolysis reaction is carried out in thepresence of less than stoichiometric amounts of calcium ions, a calciumcompound such as the chloride, oxide, hydroxide, carbonate etc. shouldbe added in amounts at least sufficient to provide for thestoichiometric amount required for complete precipitation of allpotential fluoride produced by the hydrolysis. It is also preferred tomaintain the pH during this reaction step in the range from about 8.0 to11.0. The reaction proceeds well at ambient temperatures; therefore, areaction retention time of about 10 to 20 minutes is usually adequateunder conditions of proper agitation to provide intimate contact ofreactants. The precipitated calcium fluoride is subsequently removedfrom the reaction mixture by any solids-liquid separation techniqueknown in the art.

The process of this invention can be used to treat spent fluoroborateprocess solutions and rinse waters associated with such processing.Additionally, this system may receive and treat the effluent from otherprocesses wherein metal fluoroborate solutions are subjected totreatment for removal and for recovery of contained metals such as tinand lead fluoroborate. Systems receiving effluents from a variety ofsources can be envisioned to function on a batch, flow-through, orintegrated treatment basis.

The final liquid effluent from the process may be safely disposed ofwithout causing any of the pollution problems previously associated withwaste streams from operations employing fluoroborate solutions. Also,disposal of calcium fluoride is not a problem. If desired, the calciumfluoride may be used as a starting material for various reactions, suchas in the production of hydrofluoric acid or as a flux in metalrefining.

Reference is now had to FIG. 1, which depicts a typical batch operationof the process of the invention. Into a closed reactor vessel 1 equippedwith means for agitation 2, a heat source 3 and an exhaust 4 isintroduced a desired quantity of the waste stream 5 of known dissolvedfluoroborate concentration. An appropriate quantity of calcium ions areadded in line 6 and, if necessary, an acid or a base is introduced inline 7 to maintain the pH in the desired acid range. The reaction isallowed to proceed at elevated temperatures and under agitation. Vaporsleaving the reaction vessel through exhaust 4 are suitably scrubbed in ascrubber (not shown) to remove volatilized hydrofluoric acid liberatedin the reaction. After the hydrolysis reaction is completed, heating isdiscontinued and the pH is adjusted to a value in the alkaline range byintroduction of a base through line 7 and optionally by addition offurther calcium oxide or hydroxide through line 6. Calcium fluoride isthereby precipitated, which after the end of the reaction is removed asa slurry by means of pump 8 and line 9 to a solids/liquid separationzone not shown on the drawing.

FIG. 2 shows another embodiment of the process of the invention, whichis carried out under continuous flow through conditions. The hydrolysisreaction is carried out in very much the same way as in the batchoperation illustrated in FIG. 1, except that the waste streamintroduction and the calcium ion addition to reactor 1 is on acontinuous basis. The reactor is also equipped with overflow means 10,which enables the effluent 11 from the hydrolysis reactor 1 to flowdirectly into closed neutralization reactor 12. Hydrolysis reactor 1 issized to provide the proper average residence time of the reactionmixture therein. For the neutralization reaction a suitable base iscontinuously added in line 13 to provide the alkaline conditionsnecessary for the precipitation of calcium fluoride. The reactor contentis agitated by agitator means 14 therefor. The exhaust 15 from reactor12 and exhaust 4 from reactor 1 are scrubbed in scrubber 16 to removeany volatilized hydrofluoric acid and then released to the atmosphere inline 17. The agitated slurry in reactor 12 is removed through overflowmeans 18 and line 19 into clarification tank 20 where precipitatedcalcium fluoride is allowed to settle. In a case where the waste stream1 is a solution containing a metal fluoroborate, the precipitate inclarification vessel 12 will also contain a certain amount of thecorresponding metal hydroxide. The supernatant liquid is withdrawnthrough overflow means and discharged by means of conduit 22.

FIG. 3 shows the use of this invention as integrated into a finishingscheme. In this method, workpieces flow through a series of separateclosed-loop recirculated rinses, and solution transfer from onesequential loop to another occurs through dragout on the workpieces. Thepresent invention is applied to this type of treatment as a hydrolysisrinse followed by a neutralization rinse. These reactions do notnecessarily occur at the rinse station, but are usually performed in aremote vessel where conditions are maintained to achieve the desiredreaction. After appropriate retention and treatment, the effluents fromthe remote reaction sites are continuously returned for reuse at therespective rinse station.

For example, FIG. 3 could represent a metal fluoroborate plating systemwith integrated metal recovery and integrated fluoroborate treatment.Work pieces removed from the plating bath 50 are allowed to travel inline through the sequential rinses as shown by the work flow line 51.Fluoroborate plating solution is rinsed from the work in vessel 52 in arecirculated recovery solution 53. This rinse is continuouslyrecirculated to a recovery cell 54 equipped with electrodes 55. Metalions from the plating bath are electrolytically removed from solutionand the effluent from the cell is returned via pump 56 to the rinse witha diminished metal content. In an alternate embodiment for metalrecovery not shown, the loop comprising vessel 52 and recovery cell 54can be omitted, while treatment vessel 58 is equipped with electrodes,thereby achieving simultaneous metal recovery and hydrolysis in saidvessel 58. Drag-out from the metal recovery rinse enters therecirculated fluoroborate hydrolysis system via rinse vessel 57. In thisloop, the appropriate conditions are maintained for fluoroboratehydrolysis in a remote treatment vessel 58 by means of heat 59, calciumion addition 60 and pH control 61. The effluent solution 62 fromhydrolysis (laden with freed fluoride and hydrofluoric acid) is returnedvia pump 63 to the rinse vessel 57 where the drag-out mechanism willtransfer the freed fluoride and hydrofluoric acid into the recirculatedneutralization rinse 64 in rinse tank 65. In the remote treatment vessel66 pH is adjusted by means of introduction of a base in line 67. Vessel66 is divided into three separate compartments 67, 68 and 69, insequential overflow communication with one another. Compartment 67 isequipped with agitator 69 and its function is the same as that of vessel12 in FIG. 2. Similarly, settling compartment 68 functions as vessel 20in FIG. 2. Clarified rinse is pumped from compartment 69 by means ofpump 70 to rinse vessel 65.

Some precipitation of calcium fluoride may occur in the hydrolysisvessel 58, which for that reason can be compartmentalized into threezones 71, 72 and 73 in the same fashion as shown for vessel 66. Theprecipitate collected in compartment 72 is transferred via pump 74 andconduit 75 into compartment 67 of vessel 66 for neutralization ofentrained acid and final solid-liquid separation in zone 68, providedwith outlet 79 for withdrawal of precipitated solids. Vapors from vessel58 are introduced beneath the liquid surface of vessel 66 throughconduit 76. The workpiece is subjected to a water rinse in vessel 77 andspent rinse water is discharged through line 78.

A refinement not shown on FIG. 3 would involve a mechanism for directsolution transfer from the metal recovery rinse system to thefluoroborate hydrolysis center. This would permit a periodic orcontinuous "blow-down" of the recovery rinse as a control on thefluoroboric acid in this loop. This type of blow-down would be necessarywhere drag out volumes are insufficient for removal of the acidliberated during electrolytic recovery and build up of free acid couldinterfere with electrolytic metal recovery.

To demonstrate the interplay of variables (time, temperature, calciumconcentration of pH), and to illustrate other potential conditions forthis fluoroborate hydrolysis scheme, a series of batch experiments(Examples I through IV) were conducted wherein conditions oftemperature, pH and calcium concentration were varied and the rate offluoroborate hydrolysis was monitored. Equipment was used substantiallyas shown in FIG. 1 with the exception that the volatiles were condensedand returned to the reactor, thereby preventing loss offluoride-containing compound from the system. The hydrolysis rates weredetermined by total fluoride analyses performed on aliquote samples ofthese test solutions. These samples were taken from treatment systemsconducted under the general conditions described by equation (1) andthen treated with sodium hydroxide so as to provide a final pH in therange of 8.0 to 9.0. In those cases where the reaction solutioncontained insufficient calcium for total fluoride precipitation, calciumchloride was added on neutralization to provide at least thestoichiometric amount of calcium requisite for complete precipitation ofall potential fluoride contained in the sample. The two reactions,hydrolysis and neutralization, are summarized by the following equation:

    HBF.sub.4 + 2CaCl.sub.2 + 4NaOH → B(OH).sub.3 + 2CaF.sub.2 + 4NaCl + H.sub.2 O                                                 (4)

in addition, it should be noted that in the examples to be discussed,where percent hydrolysis of BF⁻ ₄ was judged by fluoride removal, allreported results were adjusted for the appropriate, slight calciumfluoride solubility at the reported pH value.

EXAMPLE I

Four solutions (A through D), each containing 23 m moles of fluoride asfluoroboric acid in 500 ml of deionized water, were placed in separateplastic beakers. Calcium chloride was added to these samplesrespectively so as to provide a calcium ion concentration of 1.5, 0.5,0.25 and 0.0 times the potential molar fluoride value available oncomplete hydrolysis by the fluoroboric acid. All were heated toapproximately 180° F. and samples were taken periodically for analysis.These samples were treated as described above for adjustment of pH and,where necessary, with calcium addition; then filtered and analyzed fortotal fluoride. Throughout the test period, the pH of all hydrolysissolutions remained in the range of 1.5 to 2.5; therefore, no additionswere necessary to keep this parameter relatively constant. Pertinentdata are shown in Table 1 and FIG. 4, which displays the results of thisstudy as percent fluoroborate hydrolysis (removal of potential fluoridevalues from solution) versus hydrolysis reaction time. This plotillustrates the improvement had on hydrolysis when the reaction iscarried out in the presence of calcium ions. Where, at least, thestoichiometric amount of calcium necessary for complete fluorideprecipitation was present in the hydrolysis reaction, fluoroboratebreakdown was complete in 1 hour or less.

                  TABLE 1                                                         ______________________________________                                        Effect of Calcium Ion Concentration on % Hydrolysis                                      Ca ion concentration - PMFV                                        Time - hrs.  0       0.25     0.5    1.5                                      ______________________________________                                        0.5          43      66.5      90     91                                      1.0          56      80.4     100    100                                      1.5          56      86.9     100    100                                      2.0          56      86.9     100    100                                      5.0          56      86.9     100    100                                      ______________________________________                                    

EXAMPLE II

To illustrate dependency of fluoroborate hydrolysis upon reactiontemperature, four 500 ml samples (E through H), each containing 23 mmoles fluoride as fluoroboric acid and 11.5 m moles of calcium ascalcium chloride, were subjected respectively to temperatures of 65°,130°, 160°, and 180° F. As in Example I, these reactions wereperiodically sampled, treated and analyzed for total fluoride. Again,the pH of all test solutions remained in the range of 1.5 to 2.5, and noadjustment of this parameter was required. The pertinent data arepresented in Table 2 and graphed in FIG. 6. As shown, use of elevatedtemperatures beneficially affects the hydrolysis rate and completehydrolysis can be achieved in 1 hour or less when the hydrolysisreaction temperature is maintained at about 180° F.

                  TABLE 2                                                         ______________________________________                                        Effect of Temperature on % Hydrolysis                                                    Temperature - ° F                                           Time - hrs.  65      130      160    180                                      ______________________________________                                        0.5          17.9    24.3     46.1    90                                      1.0          22.0    34.8     73.9   100                                      2.0          30.5    53.9     88.7   100                                      3.0          --      67.8     --     100                                      4.0          32.6    67.0     92.2   100                                      ______________________________________                                    

EXAMPLE III

Three solutions (I through K), containing 23 m moles fluoride asfluoroboric acid and 11.5 m moles of calcium (added as calcium chloride)in 500 ml of deionized water, were heated and maintained at atemperature near 180° F. During this process, the pH of solutions I, J,and K were maintained respectively at the approximate pH's of 1.8, 6.2and 8.9 by appropriate additions of sodium hydroxide. As in Examples Iand II, periodic samples were taken from these reactions and, wherenecessary, adjusted to a pH of about 8.0 to 9.0. Subsequently, thesesamples were filtered and analyzed for total fluoride. Results of thisreaction series are shown in Table 3 and represented in FIG. 5. Asshown, maintenance of acid conditions promotes the hydrolysis reactionand rapid rates are obtained in the acidic pH range.

                  TABLE 3                                                         ______________________________________                                        Effect of pH on % Hydrolysis                                                               ph                                                               Time - hrs.    1.8       6.2       8.9                                        ______________________________________                                        0.5             90       39        35                                         1.0            100       51.4      44                                         1.5            100       54        48                                         2              100       57        49                                         5              100       66        50                                         ______________________________________                                    

EXAMPLE IV

To further define the optimum pH conditions for fluoroboratedestruction, another series of experiments was conducted according tothe conditions and procedures described in Example III. However, in thisseries, individual test solutions were maintained at pH values ofapproximately 0, 0.5, 1.0, 3.0, and 4.0 and the time to achieve completefluoroborate hydrolysis was again judged by total fluoride analysisperformed on aliquote samples of test solutions. Results of this studyare shown in Table 4 and are also displayed in FIG. 7 as a plot of timerequired for complete fluoroborate hydrolysis versus pH of the reactionsolution. The hydrolysis time shown on FIG. 7 for pH equal 1.8 wasestimated from the test described in Experiment III, and all valuesshown are somewhat approximate as analyses were performed at 30-minuteintervals-- the desired hydrolysis reaction most likely was complete ina shorter time period than shown in FIG. 7. However, these data serve toillustrate that fluoroborate decomposition proceeds very rapidly in thepreferred pH range.

                  TABLE 4                                                         ______________________________________                                        Effect of pH on Time for                                                      Complete Hydrolysis                                                           pH               Time - hrs                                                   ______________________________________                                        0                1.5                                                          0.5              1.5                                                          1.0              1.0                                                          3.0              1.0                                                          4.0              2.0                                                          ______________________________________                                    

EXAMPLE V

To demonstrate the fluoroborate treatment method of this invention inother than a batch system, a laboratory-scale continuous flow-throughtreatment was set up to approximate the scheme shown in FIG. 2, anexception being that in the laboratory system, F. - F. the hydrolysistank was capped and vented into the neutralization tank. The wastestream feed to the hydrolysis tank was prepared from a standard tinfluoroborate plating bath by diluting to 10% of normal concentrationwith deionized water. This solution contained approximately 32.5 g/lSn(BF₄)₂, 10.5 g/l HBF₄, and small quantities of various organicadditives usually found in this type of plating bath for improvement ofthe deposit and to stabilize the solution. Before the solution was fedinto the treatment system, it was passed through an electrolyticrecovery cell where the tin content of the solution was lowered toapproximately 2.0 g/l. The overflow from the recovery cell was directedinto a 3-liter hydrolysis tank where it was heated to 180° F-200° F andagitated in the presence of calcium ions at a pH in the range of 1.5 to2.0 for a period of 1.5 to 3.0 hours, depending upon the rate ofcontinuous addition of feed solution. Calcium ions were provided at 1.0PMFV by addition of calcium chloride solution (615-620 g/l CaCl₂.sup..2H₂ O) and calcium oxide as necessary to hold the hydrolysis solution inthe desired pH range. The overflow from hydrolysis passed into a pHadjustment vessel where the pH was maintained between 8.0 and 10.5 byaddition of lime slurry having a concentration of 20 g/l. Effluent fromthe pH adjustment tank flowed into a final container where theprecipitated calcium fluoride and tin hydroxide were allowed to settle.The effluent from this step was periodically monitored for totalfluoride and tin content and it was found that the total fluoride in theeffluent was consistently in the range of 300 to 350 mg/l, and that thetin levels in same were on the order of 1 to 2 mg/l. Total fluorideanalysis on the effluent indicated a 98 to 99 percent hydrolysis of thefluoroborate contained in the feed solution accounting for the dilutiondue to addition of calcium chloride solution and lime slurry. Presenceof the residual fluoride in the effluent was attributed to unavoidablebreakthrough or "short-circuiting" that can occur in such asmall-volume, high-load system.

What is claimed is:
 1. An integrated process for removing waste drag-outcontaining dissolved fluoroborates from work pieces that have beensubjected to in line treatment in a fluoroborate bath and for pollutionfree disposal of process effluents which comprisesmaintaining a firstrinse zone containing an acidic solution, a second rinse zone containinga neutralizing solution, and a third rinse zone containing water;continuously moving the work pieces from the fluoroborate bath into andthrough each of the first, second and third rinse zones, wherebyfluoroborate waste drag-out is substantially removed from surfaces ofthe work pieces into the acidic solution of the first rinse zone, anddrag-out from the first rinse zone is substantially removed from saidsurfaces into the neutralizing solution of the second rinse zone, anddrag-out from the second rinse zone is removed from the surfaces intothe water of the third rinse zone; continuously passing the acidicsolution containing the fluoroborate waste drag-out from the first rinsezone to a first treatment zone maintained at an elevated temperature ofat least 130° F and at a pH of about 4 or less adding calcium ions tothe first treatment zone to liberate fluoride values from thefluoroborate drag-out, wherein the total amount of calcium ions in thefirst treatment zone is sufficient to provide at least 0.25 times thepotential molar fluoride value of the fluoroborate drag-out;recirculating the acidic solution containing liberated fluoride valuesto the first rinse zone for further removal of fluoroborate wastedrag-out; continuously passing from the second rinse zone theneutralizing solution containing the drag-out from the first rinse zoneincluding liberated fluoride values to a second treatment zone;maintaining sufficient alkaline conditions in said second treatment zoneto precipitate calcium fluoride; recirculating the neutralizationsolution depleted in fluoride values to the second rinse zone forfurther removal of drag-out from the first rinse zone; recoveringprecipitated calcium fluoride from the second treatment zone, andwithdrawing spent rinse water from the third rinse zone.
 2. The processof claim 1, wherein the fluoroborate bath comprises metal fluoroboratesand metal values are recovered as precipitated hydroxides together withcalcium fluoride from the second treatment zone.
 3. The proces of claim1 wherein the fluoroborate bath comprises metal fluoroborates andwherein metal values are electrolytically recovered from thefluoroborate waste drag-out.
 4. The process of claim 3 wherein theelectrolytic recovery is carried out in the first treatment zone.
 5. Theprocess of claim 3 wherein the electrolytic recovery is carried out bymaintaining a fourth rinse zone containing a rinse solution, which zoneis in communication with an electrolytic cell for metal recovery, andthe work pieces are moved from the fluoroborate bath into and throughsaid fourth rinse zone into the first rinse zone; metal fluoroboratewaste drag-out is substantially removed from the surfaces of the workpieces into the rinse solution; rinse solution containing the metalfluoroborate drag-out is removed to the electrolytic cell; metal valuesare recovered in said electrolytic cell; and metal depleted rinsesolution containing fluoroborate is recirculated to the fourth rinsezone.